“To exploit the full potential of maize it will be essential to adjust the diet as feed quality changes, but equally it will be important to monitor stocks closely to ensure they last until turnout.”

Dr Homer says the latest analysis of 2018 maize crops confirms that most farmers produced good quality silage. While the analysis will remain fairly consistent throughout the clamp, she says the parameter farmers need to monitor through regular, at least monthly, analysis of silage is starch degradability which affects how the energy in maize is used.

She explains that starch degradability increases with time in the clamp, as the zein/ protein matrix which surrounds the maize starch granule is broken down by the acids in the clamp allowing bacteria to utilise the starch. The longer maize silage spends in the clamp the more degradable the starch becomes until it plateaus after approximately 8-10 months after ensiling.

“Before degradability is increased the rumen bacteria have to work harder to release the starch in the limited time it spends in the rumen, so changing degradability significantly alters how the energy in maize is used.

“With increased degradability, we see an increase in both Total Fermentable Carbohydrate in the rumen (TFC) and also the Rapidly Fermentable fraction (RFC). At the same time, as more starch is fermented in the rumen we see a reduction in the proportion of bypass starch.

“While the ME of the silage will remain unchanged, the Dynamic Energy which reflects the full performance of energy increases due to more energy being available in the rumen while the bypass starch is more digestible in the intestine and so can be used more effectively by the cow.”

Dr Homer emphasised that regular analysis such as that carried out by Trouw Nutrition is important as the rate of increase in degradability will be influenced by the growing season.

In 2018 the high temperatures and increased sunlight hours meant crop development was generally more rapid. This lead to cobs filling well and ripening quickly so the protein matrix did not get time to form fully. The result was some maize crops had high degradability as soon as clamps were opened.

“Dry matter content also plays a part. Wetter silages tend to be more fermentable at the start of the season while higher dry matter crops are less degradable initially but are more changeable over time.”

The average starch degradability is the Trouw Nutrition sample is 79.2% but the range is from 55-85%. Samples with a dry matter content of 55% are averaging a starch degradability of less than 60% while samples at 25%DM are more than 80% degradable, meaning they will feed very differently.

Regionally this year Dr Homer says they have seen generally drier, more lignified samples in the south west with lower starch degradability while crops in the north have performed well because they received more sun than usual and have been more fermentable immediately.

While stressing that all these factors will influence the rate at which starch degradability will increase, she says that for the average analysis with 33% DM and degradability currently at 80%, the prediction would be for this to be around 84% later in January. Table 1 shows what this will mean for rumen fermentation.

“As degradability rises the amount of starch fermented in the rumen increases while the bypass proportion declines. What we see is an increase in potential acid loading which could be a problem in diets where cows are already on an acidosis knife edge.

“Armed with a new analysis, diets can be revised to manage energy sources. In many cases I can foresee an opportunity to reduce other sources of RFC and TFC such as cereals, while it may be necessary to add a bit more bypass starch from rolled cereals, maize grain and potentially some byproducts if managed correctly in the diet.

“One other option this year might even be to trim back maize silage in the diet to preserve stocks.”

Dr Homer urges farmers to re-assess stocks as they head into the second half of the winter. She says comments from growers suggest yields were down last year which will have affected total stocks.

“The last thing you want to do is to run out early so measure the clamps and check stocks. Be realistic about waste. Not all the silage in the clamp will be fed so make an allowance for at least 10% waste. This could be as large as 25% in poorly managed clamps.

“Then get a new analysis so you know the dry matter of the feed. Calculate the tonnes of dry matter available and work out how long it will last at your current daily usage. Hopefully the planning at the start of the season means it will last until turnout.

“If you are going to run short, the sooner you trim usage, the less significant will be the impact on the diet and the cows. For example, can you cut maize back or out of the late lactation diet, leaving more for the fresh calvers and high yielders?

“Careful planning now combined with regular analysis will be the fundamentals to getting the most from maize in the second half of the winter,” she advises.